Plastic tray structures

ABSTRACT

A thermoplastic tray characterized by having a series of valleys and ridges arranged on the surface thereof in a herringbone-type pattern. The depth and width of the valleys and ridges, the longitudinal extent thereof, and the angular relationship of rib segments are substantially uniform and selected to achieve maximum tray rigidity in the longitudinal, transverse and diagonal directions of the tray structure.

United States Patent 72] Inventor William J. Clayton Fairport, N.Y. [21}Appl. No. 758,968 [22] Filed Sept. 11, 1968 [45] Patented Feb. 16, 1971[73] Assignee Mobil Oil Corporation [54] PLASTIC TRAY STRUCTURES 5Claims, 10 Drawing Figs. [5 2] 0.8. CI. 229/25; 220/72, 220/74; 99/ 174;220/97 [51 Int. Cl. 865d 1/00, 865d 7/42 [50] Field of Search 226/25;220/74, 97 (C), 72; 99/174 [56] References Cited UNITED STATES PATENTS1,945,397 1/1934 Gray (220/72) Primary Examiner-George T. HallAttorneys- Oswald G. Hayes, Andrew L. Gaboriault and James D. TierneyABSTRACT: A thermoplastic tray characterized by having a series ofvalleys and ridges arranged on the surface thereof in a herringbone-typepattern. The depth and width of the valleys and ridges, the longitudinalextent thereof, and the angular relationship of rib segments aresubstantially uniform and selected to achieve maximum tray rigidity inthe longitudinal, transverse and diagonal directions of the traystructure.

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PATENTEU FEB] 8197i SHEET 3 BF 3 PLASTIC TRAY STRUCTURES I. Field of theInvention The present invention relates to thermoplastic trays which areespecially adapted for the packaging of fresh meats and produce. Thesubject trays are constructed in such a manner as to allow forrelatively free circulation of air at the interface of the tray surfaceand the product packaged therein, as well as providing a means toentrain the natural juices and liquids normally exuded from the productswhich are packaged therein.

2. Description of the Prior Art meats In recent years, it has becomecommonplace in the retail sales of fresh meats and produce, to package,for example, fresh cuts of meat in individual consumer size packages.Such packages are generally characterized as comprising a shallow,rectangular support tray, the product being retained in this supporttray by being overwrapped with a transparent material such as, forexample, cellophane or polyethylene film material and the like.

In the past, such support trays have been fabricated from materials suchas molded fibrous pulp or thermoplastic materials, polystyrene havingbeen found to be a preferred plastic for the latter type of tray. In thecase of molded pulp trays, it has been found that ,whenmoisture-containing products are packaged therein, the absorbtive natureof the pulp material has a severe dehydrative effect on products such asfresh meat, and, likewise, such water absorption into the pulp fibers ofthe tray has a weakening effect on the tray structure. It has been foundthat when support trays are fabricated from plastic materials, theaforenoted deficiencies of pulp trays are eliminated to a great extent.However, in the case of plastic trays which are relatively impervious tothe passage of air and moisture vapor, there is a tendency for thatportion of the meat in contact with such a plastic tray to rapidlydiscolor, losing its natural bloom and resulting in the containedproducts having an unpleasant and unappetizing appearance from theconsumers point of view.

Attempts have been made in the past to remedy the aforenoteddeficiencies in plastic packaging trays, for example, as disclosed inU.S. Pat. No. 2,918,379 by perforating the tray bottom to provideventilation holes therethrough. More commonly, as disclosed for examplein U. S. Pat. No. 3,151,799, prior art attempts to reduce suchdiscoloration consisted in reducing the surface area of the tray bottom,which was in contact with the meat product supported thereon. Asdisclosed in U.S. Pat. No. 3,ll,799 this reduction in interfacialcontact between the tray bottom and meat product supported thereon maybe achieved by embossing the tray bottom to provide a series ofelongated, upstanding projections separated by relatively flat traybottom portions, whereby the meat now rested on only the upper surfaceof the upstanding projections rather than on I00 percent of tray bottomsurface. Such an arrangement allows for the circulation of airintermediate the upstanding projections, whereby the natural bloom ofthe meat product may be preserved for relatively long periods of time.

It has been found, however, that such prior art trays as aforediscussedare not entirely satisfactory. In the case of plastic trays which havebeen perforated to allow for adequate product ventilation, productspackaged therein may become prematurely dehydrated as a result ofmoisture loss through such ventilation holes. Additionally, suchapertures in the tray bottom may result in undesirable seepage ofliquids therethrough. In the case of the aforediscussed prior art traystructures wherein the tray bottoms have been embossed to reduce thetray contact area, it has been found that there is a tendency for suchtrays to bend or collapse along lines corresponding to the embossedridges in the tray bottom. Such a tendency is especially prevalent inthe case of trays formed from relatively thin plastic sheet material onthe order of less than about 20 mils, for example.

SUMMARY OF THE INVENTION The plastic trays of the present inventioncomprise a generally rectangular bottom surface surrounded by fourupstanding and adjoining tray walls which are integral extensions of thetray bottom. The surface of the tray bottom is characterized by having aseries of contiguous valley segments and contiguous ridge segmentsarranged thereon in a preselected pattern which simulates a herringbonetype of design. The depth and width of the valleys and the ridges aresubstantially uniform and preselected, dependent upon desired traythickness and size, to achieve maximum tray rigidity in both thelongitudinal, transverse and diagonal directions of the tray structure.In addition, the valleys in the surface of the tray bottom serve toentrain liquids exuded from moisture-emitting products containedtherein; and the ridges provide a discontinuous supporting surface ofminimal contact area allowing for relatively free circulation of air onthe undersurface of the packaged product.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a plastic trayconstruction in accordance with the present invention.

FIG. 2 is a side elevational view of the tray shown in FIG. 1.

FIG. 3 is an end elevational view of the tray shown in FIG. 1.

FIG. 4 is an enlarged fragmentary cross-sectional view of the tray shownin FIG. I and taken along the reference line 44 thereof, and furtherillustrating a meat product and a film overwrap.

FIG. 5 is an enlarged fragmentary cross-sectional view of the tray shownin FIG. I and taken along the reference line 5-5 thereof.

FIG. 6 is a top plan view of a modified form of a tray constructed inaccordance with the present invention.

FIG. 7 is a side elevational view of the tray shown in FIG. 6.

FIG. 8 is a schematic illustration, illustrative of modifications ofcorner portions of the tray illustrated in FIG. 6.

FIG. 9 is a fragmentary cross-sectional view of two nested trays andillustrative of the tray corner modifications schematically depicted inFIG. 8.

FIG. 10 is a top plan view of a still further modification of the trayconstructions according to the principles of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS The tray structures of the presentinvention are formed from moisture-resistant plastic material.Thermoplastic or thermosetting resin polymers may be employed tofabricate the structures of the present invention, however,thermoplastic materials are preferred. Suitable thermoplastic resinsinclude vinylaromatic polymers such as polystyrene; polyolefins such aspolyethylene, polypropylene, polybutene, etc. polyvinyl chloride,polyvinylidene chloride, rubber hydrohalides, polyesters and copolymers,and mixtures of these resins.

Standard forming techniques such as, for example, vacuum or blow moldingmay be employed to form the tray structures of the present inventionfrom preformed plastic sheet. Alternatively, the trays may be formeddirectly from unformed resinous materials utilizing, for example,injection molding or rotational molding techniques. As hereinbeforediscussed, the novel tray structures of the present invention comprise arectangular bottom wall surrounded by four integral and upstandingsidewalls. A preferred material of construction for the tray structuresof the present invention has been found to be oriented polystyrene film.The thickness of the tray structure may vary within wide limits,principally dependent upon the end use intended for such trays. However,for purposes of the present invention, polystyrene film thicknesses onthe order of from about 3 mils to about 30 mils, and preferably fromabout 5 mils to about 15 mils, have been found to be satisfactory.

When smooth, flat bottom trays are fabricated from such film material,the trays have a very neat and attractive appearance. However, suchtrays are impractical in that, in addition to causing productdiscoloration as aforediscussed, they lack the requisite rigidity forpackaging applications. For example, when slight compressive forces areapplied either in the transverse or longitudinal direction or obliquelyacross the tray from corner to corner, the tray has a tendency to buckleand collapse in the direction of the applied forces. It has been foundthat when the bottom surface of such trays are embossed to providetherein a series of ridges and valleys, the tray becomes more rigid,resisting deformation forces applied thereto. It has further been foundthat when elongated parallel ridges extending in the transversedirection of the tray are embossed in the tray bottom, such transverseridges effectively resist deformation forces applied across the tray ina direction parallel to such ridges. However, when deformation forcesare applied longitudinally to such an embossed tray, for exampledistortional forces perpendicular to said transverse ribs, there is adefinite tendency for the tray to buckle and fold along lines generallyparallel to such transverse ribs. Applicant has found, likewise, thatwhen such trays are fabricated with the embossed upstanding parallelribs extending longitudinally of said tray, the tray is strengthened inthe longitudinal direction. However, when compressive forces are appliedtransversely of the tray, the tray will buckle and bend along thelongitudinally extending ribs.

In an effort to remedy the structural deficiencies of the aforediscussedembossed trays, trays were constructed wherein a plurality ofcrisscrossing, upstanding ribs were embossed in the tray bottom. Aportion of these ribs extended parallel to one another in a longitudinaldirection from end-toend of the tray. The other portion of the ribsextended, parallel to one another, transversely across said longitudinalribs and from side-to-side of said tray, whereby a checkerboard" ribpattern was embossed upon the tray bottom. Although such an embossmentpattern proved to be superior to the aforediscussed embossed traydesigns in that it exhibited greater resistance to structuraldeformation forces, in both the longitudinal and transverse direction ofthe tray, such an arrangement resulted in weak spots in the tray atthose portions in the tray bottom where longitudinal ribs intersectedthe transverse ribs resulting in unsatisfactory tray strength.

Referring now to an embodiment of the structure as illustrated in FIG.I, applicant has found that by arranging upstanding, elongated, spacedapart ribs 11, embossed in the internal bottom surface of the tray inthe form ofa herringbone pattern wherein each of the ribs comprised aseries of contiguous rib segments, each of said segments meeting anadjacent segment at an angle of approximately 90, support trays may beformed which exhibit outstanding strength characteristics as well asother desirable packaging characteristics, as will be more fullydescribed hereinafter. The herringbone, or chevron, ribbed patternembossed on the bottom surface of the tray structures of the presentinvention results in an extremely rigid tray which will resistdeformation forces applied to the tray in either a longitudinal ortransverse direction, and, since there is no crisscrossing of the ribs,weak sport spots in such a tray bottom are nonexistent.

Additionally, it has been found that overall tray stiffness is dependentto a great extend upon the number of upstanding ribs which are embossedin the tray bottom. Since the chevron rib arrangement illustrated inFIG. 1 results in a maximum number of rib segments per given area oftray bottom, and since such rib segments extend in directions whichimpart, simultaneously, strength in both longitudinal and transversedirections, the resultant tray structure is one which, for equivalentamounts, i.e. weight, of construction material, is far superior to anyhitherto commercially available support trays.

Although, as hereinbefore outlined, it is extremely desirable in traysof the type herein contemplated to exhibit as much rigidity as possiblein both the longitudinal and transverse direction, as well as diagonallyacross the tray structures, it

will be understood that, by virtue of the relatively thin material fromwhich the subject trays are fabricated, a certain degree of flexure ofcomponent parts of the tray structure, e.g. the tray sidewalls, willinevitably occur during normal handling and usage of such trays.Accordingly, it is essential that such flexure results in the sidewallsbending and not breaking or buckling. As a result of the novelconstruction of the tray structures of the present invention, there isprovided a plurality oflocations, at points along the side and endwallsof the tray structures, which act to distribute bending stresses appliedthereto across substantially the entire tray length or width, wherebysingle stress points are eliminated which would otherwise result in thetray breaking or buckling when forces are applied to the walls thereof.

It will be obvious to those skilled in the art that the specificdimensions and spacing of the individual contiguous rib segments mayvary within wide limits. It has been found, however, for purposes of thepresent tray structure, that the spacing between ribs may vary fromabout 0.12 inch up to about 2 inches, and is preferably about 0.25 inch.The height of the individual rib segments is preferably at least abouttwo thirtyseconds of an inch and more preferably about threethirtyseconds of an inch.

As illustrated in FIG. 1, the angle that is formed at the apex of thechevron formed by the individual contiguous rib segments is optimallyabout 90. It has been found that an angle of about 90 results in a traywhich exhibits relatively balanced strength, i.e. rigidity, in both thetransverse and longitudinal direction. However, this angle may varywithin limits from about 60 to about 120, and preferably from about toabout 100, dependent upon packaging applications intended therefor,without too great an adverse effect on the overall requisite rigidity ofthe tray. It has been found that when this angle is reduced to 60, theend-to-end stiffness increases about I00 percent and the side-to-sidestiffness is decreased to about 50 percent as that exhibited by a trayhaving the rib segments merging at a angle. Conversely, when this angleis increased to 120, the side-to-side stiffness is increased aboutpercent and the end-to-end stiffness is decreased by about 50 percent.

It will be noted from FIG. 1, and as specifically illustrated therein,that sets of ribs, each set comprising a series of four coextensive ribsegments (a, b, c and d) extend completely across preselected areas ofthe tray bottom surface. The length of each of these individual ribsegments may vary dependent upon the transverse dimension of the trayand are preferably from about 1 inch to about 1.5 inches in length. Itis within the purview of the present invention to provide in the bottomof the tray structure any number of such contiguous rib segments from atleast about two up to about 20 or more. In the case of relatively widepackaging trays, i.e. on the order of more than 10 inches in width, ithas sometimes been found desirable to limit the length oftheseindividual rib segments up to a length of less than about Z /inches andpreferably less than 2 inches. Longer rib segment lengths have beenfound to result in the undesirable tendency of valleys 12 to buckleupwardly into the tray interior when pressures encountered in normaltray handling and usage are applied to the undersurface of the tray.

As hereinbefore noted, in addition to imparting strength to the tray,the upstanding chevron rib pattern in the bottom of the present traysprovides air spaces, in the form of valleys 12 intermediate theupstanding support ribs 11 for circulation of air therethrough tominimize product discoloration and to maintain the natural bloom of meatproducts packaged thereon. It will be apparent that such interribspacing likewise allows for continuous valleys 12 to entrain liquidsexuded from the meat products packaged in such trays resulting in aneater appearing package.

It will also be noted, particularly from FIGS. 2 and 3 of the drawings,that upstanding ribs 11 embossed in the bottom surface of the tray,rather than terminating at the juncture of the tray bottom with theupstanding sidewalls of the tray, may extend further upwardly,preferably substantially vertically, into the sidewalls l3 and endwalls.14 whereby the side and endwalls 13 and 14 are further rigidified. Ithas been found that satisfactory widewall strength may be achieved byextension of the embossed ribs up the tray sidewalls a distanceequivalent to at least one-third of the tray wall height.

As also shown in FIG. 1, in order to rigidify the corner portions of thetray illustrated therein, the tray may be provided with upstandingplateaus or flat areaslS. Such an upstanding area in each of the cornersof the tray structures of the present invention, although not anabsolute necessity, is desirable in those instances where it is desiredto have a tray which exhibits rigidity in the corner areas thereof.

Additionally, as more clearly illustrated in FIGS. 6, 7, 8 and 9,another embodiment of the tray structure of the present inventioncomprises providing flat or planar areas 16, in the bottom portion ofthe tray. As illustrated in FIG. 6, such flat or planar portions 16 maybe provided adjacent opposite ends of the tray structure or, althoughnot illustrated, such planar portions may be provided anywhere on thetray bottom surface, for example in the middle thereof. Planar traybottom portion 16, in addition to providing a decorative effect to theoverall appearance of the tray structures of the present invention, morepractically is provided to provide a flat, unembossed area on the traybottom whereon advertising indicia or tray size information, forexample, may be clearly imprinted or embossed.

As further illustrated in FIG. 6, the tray structures of the presentinvention may be provided with stacking lugs located in positions A, Bor C, which stacking lugs comprise relatively small recesses ordepressions located along the edge of tray corner portions 15. As moreclearly illustrated in FIG. 9, when a series of trays are nestedtogether one inside the other, these stacking feet serve to maintain aslight separation between adjacent trays whereby said trays may be moreeasily denested one from the other. Obviously, as illustrated in FIG. 9,the stacking lugs in a adjacent trays should be offset one with respectto the other, i.e. a tray with stacking feet positioned at A asillustrated in FIG. 8 is maintained separate or apart from the adjacenttray which has stacking feet located at position B as illustrated inFIG. 8.

As illustrated in FIG. 10, there is shown a still further modified formof the tray structures of the present invention comprising a tray havinga series of spaced apart reinforcing ribs 17 which are positionedparallel to one another and perpendicular to the tray endwall members14. It has been found that, especially in the case of larger size trays,i.e. trays having an increased bottom surface area which are employed,for example in the packaging of relatively large cuts of meat such asroasts and the like, there is a tendency for the endwall members 14 toflex outwardly to an undesirable extent when such large size trays arehandled with the relatively heavy meat products supported on the surfacethereof. Applicants have found that this undesirable flexure of endwallmember 14 may be eliminated or substantially reduced by formingreinforcing rib members 17, as illustrated in FIG. 10, perpendicularwith respect to the endwall members 14 of the tray and substantiallyparallel with respect to one another. As illustrated in FIG. 10,reinforcing rib members 17 extend into sidewall member 14 at one end ofeach of said reinforcing ribs and the opposite ends of reinforcing ribs17 are tied into and are integral with upstanding rib members 11 locatedin the bottom surface of the tray. Upstanding rib members 17 may beeither coextensive in height with rib members 11, or slightly higher,i.e. on the order of about one thirty-second to two thirtysecond inchhigher than rib members 11, or alternatively reinforcing ribs 17 maytaper with respect to their height relationship with upstanding ribmembers 11, whereby that portion of reinforcing rib 17 adjacent trayendwall 14 is higher than the terminal end of reinforcing rib 17 whichterminates integrally with at least one of upstanding rib members 11 andis coextensive in height at said terminal end with rib member 11.

It WIII be noted, from FIG. 5, that the sidewalls of upstanding ribmembers 11, rather than being substantially parallel, may be inclined ata slight angle to the vertical. Although not absolutely essential, suchinclination of the sidewalls of rib members 11 facilitates the removalof the tray structures of the present invention from the molds employedin their forming process.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention it will be apparent to thoseskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope of the invention.

Iclaim: I

1. A thermoplastic tray comprising an internal bottom surface withupstanding side and end wall members integrally joined thereto, a seriesof substantially parallel, elongated, spaced apart ribs extendingupwardly from said bottom surface, each of said ribs comprising aplurality of integrally joined segments forming a herringboneconfiguration, each of said segments being segments disposed at an angleof from about 60 to about 120 in relationship with its adjacent segment.

2. A thermoplastic meat tray in accordance with claim 1 wherein said ribsegments which are adjacent to said sidewall members extend upwardly ina, vertical direction into said sidewall members to a heightintermediate the lower and upper margin of said sidewalls.

3. A thermoplastic meat tray in accordance with claim I wherein saidribs are spaced apart a distance of from about 0.12 inch to about 2inches, said rib segments being approximately one to Zlfiinches long,said rib segments joining adjacent segments at an angle of about andsaid rib segments being at least two thirty-seconds inch in height.

4. A thermoplastic tray in accordance with claim I wherein saidthermoplastic is transparent.

5. A packaged food product comprising a tray, as described in claim I,and a food product supported on the inner surface of the tray bottom.

1. A thermoplastic tray comprising an internal bottom surface withupstanding side and end wall members integrally joined thereto, a seriesof substantially parallel, elongated, spaced apart ribs extendingupwardly from said bottom surface, each of said ribs comprising aplurality of integrally joined segments forming a herringboneconfiguration, each of said segments being segments disposed at an angleof from about 60* to about 120* in relationship with its adjacentsegment.
 2. A thermoplastic meat tray in accordance with claim 1 whereinsaid rib segments which are adjacent to said sidewall members extendupwardly in a vertical direction into said sidewall members to a heightintermediate the lower and upper margin of said sidewalls.
 3. Athermoplastic meat tray in accordance with claim 1 wherein said ribs arespaced apart a distance of from about 0.12 inch to about 2 inches, saidrib segments being approximately one to 2 1/2 inches long, said ribsegments joining adjacent segments at an angle of about 90* and said ribsegments being at least two thirty-seconds inch in height.
 4. Athermoplastic tray in accordance with claim 1 wherein said thermoplasticis transparent.
 5. A packaged food product comprising a tray, asdescribed in claim 1, and a food product supported on the inner surfaceof the tray bottom.